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Observations of the Transit of Mercury, May 9, 1891. 



By H. S. Pritchett. 



The observations of the Transit of Mercury, which are de- 

 scribed below, were made with the 6h in. Equatorial of the 

 Observatory of Washington University. A magnifying power 

 of 140 was used, and the shade glass employed was a combina- 

 tion of green and red which gave a soft dirty white tint to the 

 sun's disc. 



The atmospheric conditions on the afternoon of the 9th were 

 unusually good, and, although the sun was only io° high when 

 the transit began, the images were steady and distinct. Contacts 

 were observed as follows in Greenwich mean time. The filar 

 micrometer was used, and, having been set to the computed posi- 

 tion angle, it was easy to cut oft' a small segment of the sun's disc 

 within which the planet was to be expected. 



B. 



C. 

 D. 



May9,'9i. REMARKS. 



Gr. M. T. 



A. m. s. 



11 53 14.6 The time given marks the first moment when 1 i ould detect 

 a suspicious movement at the point of the sun's limb where 

 the planet was to enter. The encroaching disc of the 

 planet could not be made out as an indentation until some 

 seconds later. My impression at the time was that I had 

 observed the earliest possible moment when the planet 

 could be seen. 



11 55 17.4 -^t this instant the small disc of the planet was estimated to 

 j be exactly bisected by the sun's limb. This phase can be 

 noted with great sharpness. The time given above can- 

 not be in error, I think, by more than 5 seconds. 



11 57 29.6 The planet appeared to be in geometric contact with the 



I sun's limb. 

 11 57 49.0 The light first flashes around the disc of the planet. This is 

 probably the moment of true internal contact. 



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